The manufacturing process (A) as described below is known as the most popular method of casting copper alloy. At first, copper row material, scrap and addition elements or mother alloy including the addition elements are put in a melting furnace (an electrical furnace or a gas furnace) and then melted. Then, after all of the materials are melted, a sample for analysis is collected from the molten metal in the furnace. The chemical composition of the molten metal is determined by chemical analysis or instrumental analysis. The chemical composition is modified to be a desired chemical composition. Then, after the chemical composition is identified as desired, the casting of the copper alloy is carried out.
As the other case, there is a method in which alloy elements are added during transferring molten pure copper. The following methods are listed among them as the method (B) that adds solid, for example:
a. In the SCR method for copper alloy wire or the Contirod casting method, additional elements are added between the melting furnace and the casting machine to cast copper alloy with a prescribed composition (for instance, refer to Patent document 1).
b. A continuous casting apparatus comprises an adding tub and an adding crucible at the end of the casting line, which casts copper or copper alloy, and heat indirectly the molten metal in the crucible (for instance, refer to Patent document 2).
c. In the continuous alloy casting method comprising the steps of melting metal in a melting furnace, transferring the metal to a tub and casting with a casting mold, the tub has a retaining portion for the molten metal, and granular alloy elements are continuously thrown into the molten metal on the retaining portion (for instance, refer to Patent document 3).d. A continuous manufacturing apparatus of copper alloy comprises a heating furnace, wherein the heating furnace comprises the first adding means to add alloy elements, and a tundish down the heating furnace where molten copper is put in through a tub (for instance, refer to Patent document 4).
In other case, there are some methods (C) that molten metal are added during transferring molten pure copper. Some cases of the methods (C) are mentioned below.
e. Alloy elements are semi-molten or molten, and dropped to molten metal above a tundish during continuous casting. Thereby the chemical composition of an alloy are controlled, and homogenous molten metal is produced (for instance, refer to Patent document 5).f. The molten copper is held in a tundish in the continuously casting high conductive copper alloy, and Ni—P compound is added to the molten copper (for instance, refer to Patent document 6), in. a method of continuously casting high conductive copper alloy,g. A method of continuously casting alloy is that wires comprising alloy elements are continuously molten or semi-molten by arc discharge, and are added to molten base metal (for instance, refer to Patent document 7).
Moreover, there is known a chemical composition controlling method during continuously casting that electrical resistances of roughing wire are measured continuously, and the electrical resistances are used for feedback control. The method is that the adding of alloy elements are continuously controlled with the measured electrical resistances of roughing wire when conductive alloy is casted and rolled continuously by means of continuously adding additive elements to the molten metal (for instance, refer to Patent document 8).
Specific resistance of molten metal is generally known. For instance, in Data Book of Metal compiled by Japan Society of Mechanical Engineers, specific resistance of pure metal is described. The specific resistance of molten pure metal is greater than these of the pure metals in room temperature (refer to the Table 1 mentioned below).
TABLE 1Comparison of Specific resistanceSolid substanceMolten substanceSpecificSpecificMeltingresistanceresistancePointTemperature(μ ohmTemperature(μ ohm(degreesElements(degrees C.)cm)(degrees C.)cm)C.)Cu201.67110020.21083Ni206.84145485.01453Si202.3 × 1023141082.0—Sn2012.6100067.0 232
In addition, it is described that the specific resistance of copper alloy is changed as a function of mixing ratio between Sn and In (refer to Non Patent document 1). However it is not described to control chemical composition of copper alloy with the use of the above knowledge.
In recognizing the importance of the electrical characteristics of molten metal, there is described a method of detecting inclusions in the molten metal (especially aluminum alloy) (for instance, refer to Patent document 9). This method is to detect a decreasing amount of cross-sectional area of current pathway. That is, the method is not to detect the change of specific resistance as a function of the composition of molten metal in the current pathway.
Moreover, in the multi layer manufacturing method (F), electrical characteristics are applied to continuous casting (for instance, refer to Patent document 10). This method is one to continuously make a multi layer metal material, which has inner layer and surface layer; wherein the chemical composition of the inner layer is different from that of the surface layer. In the method, supply of the two metals in unit time is controlled with specific resistance of the metal in a mold so that the position of the boundary between the inner layer and the surface layer, which is determined with the specific resistance, is correspond to a specific position.    [Patent document 1] Japanese Patent Application Publication No. Shou 55-128353 (1980-128353)    [Patent document 2] Japanese Patent Application Publication No. Hei 06-063710 (1994-063710)    [Patent document 3] Japanese Patent Application Publication No. Hei 10-193059 (1998-193059)    [Patent document 4] Japanese Patent Application Publication No. 2006-341268    [Patent document 5] Japanese Patent Application Publication No. Shou 59-169654 (1984-169654)    [Patent document 6] Japanese Patent Application Publication No. Hei 08-300119 (1996-300119)    [Patent document 7] Japanese Patent Application Publication No. 2002-86251    [Patent document 8] Japanese Patent Application Publication No. Shou 58-065554 (1983-065554)    [Patent document 9] Japanese Patent Application Publication No. Shou 59-171834 (1984-171834)    [Patent document 10] Japanese Patent Application Publication No. Hei 05-277641 (1993-277641)    [Non Patent document 1] “Specific resistance measurement of molten Cu—In—Sn alloy”, Kita, Morita and Matsumoto, The summary of the speech in The Japanese Institute of Metals, Vol. 86, p. 166, 1980